The acute respiratory infections may trigger a severe heart attack (also known as acute myocardial infarction. MI). An earlier study has found that influenza vaccination can lower the risk of cardiovascular diseases and death (mortality) due to the flu (influenza) infection.

But the protection offered by the vaccine in the elderly people may not be as effective as in the younger people as the strength of the immunity will decline with age. That study has supported the existing international guidelines in advocating the flu shots (also known as influenza vaccines or flu jabs) to the people who are at a high risk of heart attack due to the flu (influenza) infection.

There are heart attacks even in the younger people affected by flu (influenza). As the heart attacks are extremely rare in the younger people (aged less than 35 years), researchers have suggested a link between the flu infection and a heart attack.

Researchers wanted to find out the association between acute myocardial infarction (heart attack. MI) and the laboratory-confirmed influenza infection. This is the first study showing the risk of heart attack with influenza. A Canadian self-controlled case series (SCCS) design study shows six times increased risk of severe heart attack in a person during the first seven days of laboratory-confirmed flu (influenza) infection when compared to a risk of a heart attack one year before or after.

Researchers have conducted an analytical study in about 20,000 adult heart attack patients from Ontario, Canada between 2009 and 2014, aged more than 35 years. They were diagnosed with a laboratory-confirmed influenza infection, one year before. The health records show that.

About 75 percent of them were aged more than 65 years with an average age of 77 years.

About 50 percent of them were women.

About 25 percent of them were with a history of heart attack and were hospitalized. Most of them are with the risk factors to a heart attack such as high blood pressure, high blood sugar (glucose) levels (type 2 diabetes. T2D) and high cholesterol levels.

About one-third of them had flu shots.

About 31 percent of the patients were not vaccinated against seasonal flu.

They also observed no heart attack in the patients after seven days of laboratory-confirmed flu infection.

Further analysis has found that 20 patients had a heart attack within a week of the laboratory-confirmed flu infection.

The elderly people, aged more than 65 years and affected with the flu are at a higher risk of heart attack when compared to lower age people affected with the flu.

The risk of heart attack with the infection due to influenza B strain is more when compared with influenza A strain.

Other common respiratory viruses such as human respiratory syncytial virus (RSV or HRSV), human parainfluenza viruses (HPIVs) or respiratory adenoviruses can also cause an enhanced risk of heart attack, but to a lesser extent.

The authors say that influenza infections may lower the blood pressure levels. A lower blood pressure can cause the lower amount of oxygen in the blood. The heart will start working faster (to pump more blood) to compensate for the lower oxygen level in the blood. This can cause a heart attack in the people with an early heart disease.

The infection due to influenza can also cause the inflammation in the arteries. The enhanced inflammation causes the formation of blood clots. The blood clots can increase the risk of heart attack as they prevent the blood flow to heart and heart tissues.

This study also shows a likelihood of immediate risk of heart attack within seven days with a laboratory-confirmed influenza infection. The authors say that the patients with an acute respiratory infection should take the flu shot immediately.

Researchers say that the sick people affected with the flu should take precautions such as washing their hands regularly, staying at home, taking flu shots (also known as influenza vaccines or flu jabs) and prevent the spreading of respiratory infections and influenza.

The study was funded by the following organizations.

Canadian Institutes of Health Research (CIHR), a federal funding agency for health research in Canada.

International Council for the Exploration of the Sea (ICES), Copenhagen, Denmark.

Public Health Ontario (PHO), Canada.

The lead author of the study was Dr. Jeffrey C. Kwong, MD, MSc, CCFP, FRCPC, senior core scientist, Primary Care & Population Health Research Program, Institute for Clinical Evaluative Sciences (ICES), Toronto, Canada. The study was published January 25, 2018, in the New England Journal of Medicine. Title of the article was "Acute Myocardial Infarction after laboratory-confirmed Influenza Infection." DOI: dx.doi.org/10.1056/NEJMoa1702090

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